Radio transmission device and method

ABSTRACT

A radio transmitting device and method enables reduction of an increase of CGI memories for the control channel and an improvement of the throughput of the data channel. When multiplex transmission through the control channel and the data channel is carried out and when adaptive modulation is applied to both channels, an MCS selecting section ( 108 ) is provided with one CQI table for the data channel and CQI tables for the control channel, and a table selecting MCS determining section ( 201 ) selects one of the tables depending on the transmission bandwidth of the terminal and determines the MCS of the control channel while looking up the selected CQI table.

TECHNICAL FIELD

The present disclosure relates to a radio transmitting apparatus and aradio transmission method that are used in communication systemsemploying an adaptive modulation.

RELATED ART

Presently, in 3GPP RAN LTE (Long Term Evolution) in uplink, singlecarrier transmission is gaining attention to achieve a low PAPR (Peak toAverage Power Ratio). Further, studies are conducted for a scheme toperform “adaptive modulation (AMC: Adaptive Modulation and Coding)” forselecting a user-specific MCS (Modulation and Coding Scheme) patternaccording to a CQI (Channel Quality Indicator) of users to achieve highthroughput.

Further, to adopt adaptive modulation and hybrid ARQ to a downlink datachannel, in uplink channel, downlink CQI information and downlinkACK/NACK information are transmitted in a control channel.

FIG. 1 shows an MCS table a terminal uses for adaptive modulation for adata channel and so on (hereinafter, “CQI table”) (see, for example,Non-Patent Document 1). Here shows, based on a CQI value, that is, basedon channel quality information including an SNR, various modulationschemes and coding rates are read from the table shown in FIG. 1 todetermine an MCS for a data channel.

Further, studies are underway to transmit an uplink data channel and anuplink control channel in the same frame, and, furthermore, to determinean MCS for the control channel at the same time as an MCS for the datachannel, using a CQI determining the MCS for the data channel (see, forexample, Non-Patent Document 2).

Accordingly, similar to the MCS for a control channel, variousmodulation schemes and coding rates (hereinafter SE: SpectralEfficiency, and SE is defined as the number of bits per symbol×codingrate) are determined in accordance with CQIs. FIG. 2 shows a concreteexample of a CQI table in which associations between data channel SE andcontrol channel SE are shown. Hybrid ARQ is not adopted to this controlchannel. Accordingly, control channel SE is set up robust with respectto CQIs that is, the SE is set up to be low such that required qualityis satisfied even in a poor reception environment.

Non-Patent Document 1: R1-073344, Nokia, “Update to 64QAM CQI tables,”3GPP TSG RAN WG1 Meeting #50, Athens, Greece, Aug. 20-24, 2007

Non-Patent Document 2: 3GPP TS36.212 V8.0.0

BRIEF SUMMARY

However, with the above-described technique, in situations where thereception environment is not poor, SE read from the table fullysatisfies required quality for a control channel, and therefore wastedradio resources are provided to use the control channel. As a result,there is a problem of decreasing data channel throughput.

This case will be explained as an example shown in FIG. 3. As shown inFIG. 3, when a data channel and a control channel are multiplexed andtransmitted in the same frame, the size of resources that can be used isdetermined. When the reception environment is not poor, SE that fullysatisfies the required quality for a control channel is set, andtherefore control channel resources are wasted. However, these wastedresources cannot be used as data channel resources, and therefore datachannel throughput decreases.

An embodiment provides a radio transmitting apparatus and a radiotransmission method that facilitates improvement of data channelthroughput.

The radio transmitting apparatus of an embodiment adopts theconfiguration including: a modulation and coding scheme selectionsection that switches associations between channel quality indicatorsand modulation and coding schemes according to a parameter of a radiocommunication terminal apparatus, to determine a modulation and codingscheme of a control channel based on the associations after theswitching; and a coding and modulation section that encodes andmodulates control data by the determined modulation and coding scheme.

The radio transmission method of an embodiment includes: a switchingstep of switching associations between channel quality indicators andmodulation and coding schemes according to a parameter of radiocommunication terminal apparatus; a modulation and coding schemeselection step of determining a modulation and coding scheme of acontrol channel based on the associations after the switching; and acoding and modulation step of encoding and modulating control data bythe determined modulation and coding scheme.

An embodiment provides an advantage of improving data channelthroughput.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows a CQI table a terminal uses for adaptive modulation of adata channel and so on;

FIG. 2 shows a concrete example of a CQI table showing associationsbetween data channel SE and control channel SE;

FIG. 3 illustrates how a data channel and a control channel aremultiplexed and transmitted in the same frame;

FIG. 4 shows the relationships between the received SNRs and the SE whenrequired BLER of a data channel is 10%;

FIG. 5 shows the relationships between the received SNRs and the SE whenrequired BER of ACK/NACK channels is 0.01%;

FIG. 6 is a block diagram showing the configuration of a radiocommunication terminal apparatus according to Embodiment 1 of thepresent disclosure;

FIG. 7 is a block diagram showing an internal configuration of the MCSselection section shown in FIG. 6;

FIG. 8 shows an example of a control channel CQI table;

FIG. 9 shows another example of a control channel CQI table;

FIG. 10 shows a block diagram showing the internal configuration of theMCS selection section according to Embodiment 2 of the presentdisclosure;

FIG. 11 shows an example of an offset lookup table;

FIG. 12 shows an example of a control channel CQI table;

FIG. 13 shows a CQI table according to Embodiment 3 of the presentdisclosure; and

FIG. 14 shows a CQI table according to Embodiment 4 of the presentdisclosure.

DETAILED DESCRIPTION

Now, embodiments of the present disclosure will be described in detailwith reference to the accompanying drawings. FIG. 4 shows therelationships between the received SNRs and the SE (Spectral Efficiency)acquired from simulation results when required BLER of a data channel is10%. Further, FIG. 5 shows the relationships between the received SNRsand the SE when required BER of ACK/NACK of control channels is 0.01%.According to the present embodiment, although the difference in areceived SNR between performance with AWGN and SE without frequencyhopping (a 180 kHz bandwidth) is 5 dB in a data channel, the differenceis 9 dB in a control channel, and therefore the focus is placed uponsevere deterioration of the control channel performance. That is, thefocus is placed upon a significant difference between the data channelperformance and the control channel performance in specific conditions.

Embodiment 1

FIG. 6 is block diagram showing the configuration of a radiocommunication terminal apparatus according to Embodiment 1 of thepresent disclosure. Now, the configuration of the radio communicationterminal apparatus will be explained with reference to FIG. 6. Radioreceiving section 102 converts a signal received via antenna 101 to abase band signal, and outputs the baseband signal to CP removing section103.

CP removing section 103 removes the CP (Cyclic Prefix) from the basebandsignal outputted from radio receiving section 102, and outputs theresulting signal to FFT section 104.

FFT section 104 performs an FFT (Fast Fourier Transform) on thetime-domain signal outputted from CP removing section 103, and outputsthe resulting frequency-domain signal to channel estimation section 105and demodulation section 106.

Channel estimation section 105 estimates a channel environment of thereceived signal using the pilot signal included in the signal outputtedfrom FFT section 104, and outputs the estimation result to demodulationsection 106.

Based on the channel environment estimation result of the outputted fromchannel estimation section 105, demodulation section 106 performschannel compensation for a signal acquired by removing controlinformation such as the pilot signal from the received signal outputtedfrom FFT section 104, that is, performs channel compensation for datainformation. Further, demodulation section 106 demodulates the signalafter the channel compensation based on the same MCS as the MCS used inthe base station of the communicating party, and outputs the demodulatedsignal to decoding section 107.

Decoding section 107 performs error correction for the demodulatedsignal outputted from demodulation section 106, and extracts informationdata sequences, CQI information and bandwidth information from thereceived signal. The CQI information and the bandwidth information areoutputted to MCS selection section 108.

MCS selection section 108 having a CQI table (described later) readsfrom the CQI table an MCS pattern associated with the CQI informationoutputted from decoding section 107, and determines the read MCS patternas the MCS for a data channel (MCS 1). Further, based on the CQIinformation and the bandwidth information outputted from decodingsection 107, MCS selection section 108 determines an MCS pattern for thecontrol channel (MCS 2) with reference to a plurality of CQI tables(described later). The determined MCS 1 is outputted to coding andmodulation section 109 and MCS 2 is outputted to coding and modulationsection 110.

Coding and modulation section 109 encodes and modulates user datareceived as input (transmission data sequences) based on MCS 1 outputtedfrom MCS selection section 108, to generate data channel transmissiondata. The generated transmission data for the data channel is outputtedto channel multiplexing section 111.

Coding and modulation section 110 encodes and modulates control datareceived as input based on MCS 2 outputted from MCS selection section108, to generate control channel transmission data. The generatedtransmission data for the control channel is outputted to channelmultiplexing section 111.

Channel multiplexing section 111 performs time-division multiplexing ofthe transmission data for the data channel outputted from coding andmodulation section 109 and the transmission data for the control channeloutputted from coding and modulation section 110. The multiplexedtransmission data is outputted to DFT-s-OFDM section 112.

DFT-s-OFDM section 112 performs a discrete Fourier transform (DFT) onthe transmission data outputted from channel multiplexing section 111and performs time-frequency transform on the data of frequencycomponents, to acquire a frequency-domain signal. Then, after thefrequency-domain signal is mapped to transmission subcarriers, themapped frequency-domain signal is subject to an IFFT (Inverse FastFourier Transform) processing, to be transformed to a time-domainsignal. The acquired time-domain signal is outputted to CP additionsection 113.

CP addition section 113 adds CPs to the frames in the transmission datasequences outputted from DFT-s-OFDM section 112 by duplicating data atthe tail of each frame and by adding the duplicated data to thebeginning of each frame, and outputs the transmission data with CPs toradio transmitting section 114.

Radio transmitting section 114 frequency-converts the baseband signaloutputted from CP addition section 113 to a radio frequency band signal,and transmits the converted signal via antenna 101.

FIG. 7 is a block diagram showing an internal configuration of MCSselection section 108 shown in FIG. 6. Based on a CQI received as input,table selection MCS determination section 201 determines MCS 2 for thecontrol channel with reference to the CQI table corresponding to thebandwidth among the control channel CQI tables shown in FIG. 8.

Based on a CQI received as input, MCS determination section 202determines MCS 1 for the data channel with reference to the data CQItable.

FIG. 8 shows an example of a control channel CQI table. Here, table 1 isthe CQI table for a 500 kHz bandwidth or below, and table 2 is the CQItable for more than a 500 kHz bandwidth. Further, with the same CQIs, SEin table 1 is set up lower than SE in table 2. When the bandwidth isnarrow as 500 kHz, that is, when frequency diversity effect is small,lower SE is selected. On the other hand, when frequency diversity effectis significant, higher SE is selected than the SE in table 1.Accordingly, when the frequency diversity effect is significant, fewcontrol signal resources make it possible to satisfy the requiredquality for the control channel compared in a case where diversityeffect is small, so that it is possible to increase the amount ofresources used for the data channel.

In this way, according to Embodiment 1, when a data channel and acontrol channel are multiplexed and transmitted and adaptive modulationis applied to both channels, by providing one data channel CQI table anda plurality of control channel CQI tables, switching between a pluralityof tables in accordance with a transmission bandwidth of a terminal, anddetermining the MCS for the control channel, it is possible to determinean MCS appropriate for the bandwidth and allocate radio resources usedfor the control channel adequately, thereby increasing radio resourcesused for the data channel. This makes it possible to improve datachannel throughput.

Although a case has been explained with the present embodiment as anexample where a CQI table is selected based only on the transmissionbandwidth, as shown in FIG. 9, it is equally possible to select four CQItables based on data channel scheduling methods in addition to abandwidth. When persistent scheduling is used for a data channel, a lowCQI is reported to make the MCS for the data channel robust. In thiscase, it is possible to increase the amount of resources used for thedata channel by taking into account the difference in CQI between twokinds of scheduling, that is, normal scheduling (i.e. dynamicscheduling) and persistent scheduling, by configuring a plurality ofcontrol channel CQI tables and making the MCS and resources of use ofthe control channel adequate.

Embodiment 2

The configuration of a radio communication terminal apparatus accordingto Embodiment 2 of the present disclosure is the same as shown in FIG. 6of Embodiment 1, this embodiment will be explained with reference toFIG. 6, and the overlapping explanation will be omitted.

FIG. 10 is a block diagram showing the internal configuration of MCSselection section 108 according to Embodiment 2 of the presentdisclosure. CQI offset MCS determination section 301 calculates acontrol channel CQI using an offset lookup table shown in FIG. 11, CQIinformation and equation 1.

Control channel CQI=CQI+Σoffset [condition]  (Equation 1)

Further, based on that control channel CQI, CQI offset MCS determinationsection 301 determines MCS 2 for the control channel with reference tothe control channel CQI table shown in FIG. 12.

FIG. 11 shows an example of an offset lookup table. Here, when the datachannel scheduling method is dynamic scheduling, the offset is zero, andwhen the data channel scheduling method is persistent scheduling, theoffset is two. In this case, offsets are provided by taking into accountof CQI differences between two kinds of scheduling, that is, betweennormal scheduling (i.e. dynamic scheduling) and persistent scheduling.

Further, the offset is zero when the data channel is used with frequencyhopping, and the offset is −4 when the bandwidth is 1 RB (resourceblock) without frequency hopping. When frequency diversity effect issmall, for example, frequency hopping is not adopted in a frame andtransmission is performed in a narrow band, the offsets are provided soas to select a lower MCS. This is because the relatively small number ofbits is transmitted and coding gain is less likely to be acquired. Bytaking into account of the above reason, offsets are provided accordingto bandwidths.

Furthermore, the offset is zero when a data channel transmission is thefirst, and the offset is −2 upon retransmissions. Received quality ispoorer than expected when a data channel is retransmitted. In such acase, received quality may deteriorate with regards to a controlchannel, and therefore an offset is provided so as to select a lowerMCS.

As explained above, according to parameters of a terminal, such as adata scheduling method, a bandwidth, frequency hopping in frames, andthe number of data channel retransmissions, it is possible to set up amore adequate MCS. Accordingly, it is possible to satisfy requiredquality for a control channel using adequate control channel resources,so that the amount of resources used for a data channel can beincreased.

FIG. 12 is an example of a control channel CQI table. Here, in additionto SE for 0 to 30 CQIs in a lookup table, lower SE for −1 to −10 CQIsand higher SE for 31 to 37 are newly set. Here, the lower SE part ismainly used when an offset is negative, and the higher SE part is mainlyused when an offset is positive.

In this way, according to Embodiment 2, when a data channel and acontrol channel are multiplexed and transmitted and adaptive modulationis applied to both channels, one data channel CQI table, one controlchannel CQI table in series formed in a larger size than that datachannel CQI table and an offset lookup table formed with parameters of aterminal are provided to determine the MCS for the control channel by aCQI found by adding all the amounts of offsets read from a offset lookuptable to a data channel CQI, so that it is possible to prevent memoryfrom increasing and improve data channel throughput.

Embodiment 3

FIG. 13 shows a CQI table according to Embodiment 3 of the presentdisclosure and by multiplying equation 1 by a scaling factor (N), arange set up in a lookup table can be bigger or smaller. A controlchannel CQI can be calculated using equation 2,

Control channel CQI=floor(N×(CQI+Σoffset[condition]))   (Equation 2)

where N is a decimal.

To apply a case where a coding scheme varies like between an uplink CQIchannel and ACK/NACK channels used in LTE, by changing the value, N, acontrol channel is applicable to different coding schemes. That is, anuplink CQI channel is applicable by only changing offset and value N,and ACK/NACK channels are applicable by an offset (N=1) only, so that itis possible to refer to MCSs of two kinds of control channels from thesame CQI table.

In this way, according to Embodiment 3, a scaling factor is multipliedby a control channel CQI that is found by adding all the amounts ofoffsets, to calculate the new control channel CQI and to determine theMCS for the control channel, so that it is possible to prevent memoryfrom increasing and improve data channel throughput even when there arecontrol channels of different coding schemes.

Embodiment 4

FIG. 14 shows a CQI table according to Embodiment 4 of the presentdisclosure. The CQI table is calculated using equation 2 shown inEmbodiment 3, where N is a decimal and, N=N_A(CQI<CQI_TH) andN=N_B(CQI>CQI_TH). Specifically, FIG. 14 shows a case where CQI_TH=3,N_A=0.7 and N_B=1.3. In this way, by changing a scaling factor, N,according to the magnitude of a CQI, it is possible to determine the MCSmore accurately.

In this way, according to Embodiment 4, by multiplying by a scalingfactor a control channel CQI found by adding all the amounts of offsets,changing the scaling factor according to the magnitude of the CQI,calculating a control channel CQI and determining the MCS for thecontrol channel, even when there are control channels of differentcoding schemes, it is possible to prevent memory from increasing, and,furthermore, improve data channel throughput.

Although cases have been explained with Embodiments 3 and 4 where aprimary linear process of multiplying N is adopted, a higher linearprocess may be adopted.

With the above embodiments, “drop” may be included in a control channelCQI table not so as to transmit a control channel using the lowest SE(MCS).

Further, with the above embodiments, when a calculated control channelCQI is outside the range of the control channel CQI table, it ispossible to use the SE (MCSs) at both ends of the CQI table or useextrapolation.

Further, although cases have been described with the above embodimentsas examples where embodiments of the present disclosure is configured byhardware, embodiments of the present disclosure can also be realized bysoftware.

Each function block employed in the description of each of theaforementioned embodiments may typically be implemented as an LSIconstituted by an integrated circuit. These may be individual chips orpartially or totally contained on a single chip. “LSI” is adopted herebut this may also be referred to as “IC,” “system LSI,” “super LSI,” or“ultra LSI” depending on differing extents of integration.

Further, the method of circuit integration is not limited to LSIs, andimplementation using dedicated circuitry or general purpose processorsis also possible. After LSI manufacture, utilization of a programmableFPGA (Field Programmable Gate Array) or a reconfigurable processor whereconnections and settings of circuit cells within an LSI can bereconfigured is also possible.

Further, if integrated circuit technology comes out to replace LSI's asa result of the advancement of semiconductor technology or a derivativeother technology, it is naturally also possible to carry out functionblock integration using this technology. Application of biotechnology isalso possible.

INDUSTRIAL APPLICABILITY

The radio transmitting apparatus and radio transmission method accordingto at least one embodiment improves data channel throughput, and isapplicable to, for example, mobile communication systems.

1. A radio transmission apparatus comprising: a coding unit configuredto code one form of control data using a modulation and coding scheme(MCS) for a data channel and an offset value, the offset value being setfor said one form of the control data; and a radio transmitting unitconfigured to transmit data in the data channel and said one form of thecontrol data coded with a coding rate according to said one form of thecontrol data.
 2. The radio transmission apparatus according to claim 1,wherein said coding unit is configured to code a first form of controldata using the MCS for the data channel and an offset value for thefirst form of the control data, and to code a second form of controldata using the MCS for the data channel and an offset value for thesecond form of the control data.
 3. The radio transmission apparatusaccording to claim 2, wherein a coding rate used to code said first formof control data is different from a coding rate used to code said secondform of control data.
 4. The radio transmission apparatus according toclaim 1, wherein said coding unit codes said one form of the controldata using a MCS determined based on the MCS for the data channel andthe offset value.
 5. The radio transmission apparatus according to claim1, wherein said one form of the control data is ACK/NACK or channelquality indicator (CQI).
 6. The radio transmission apparatus accordingto claim 1, wherein said transmitting unit multiplexes and transmits thedata and said one form of the coded control data.
 7. The radiotransmission apparatus according to claim 1, further comprising areceiving unit configured to receive control information, wherein saidcoding unit determines the MCS for the data channel based on thereceived control information.
 8. The radio transmission apparatusaccording to claim 7, wherein said coding unit codes said one form ofthe control data using the received control information and the offsetvalue.
 9. The radio transmission apparatus according to claim 7, whereinsaid coding unit codes said one form of the control data based oncontrol information, into which the received control information isadjusted based on the offset value.
 10. The radio transmission apparatusaccording to claim 7, wherein the control information is channel qualityindicator (CQI).
 11. The radio transmission apparatus according to claim1, wherein the offset value is given by multiplying a predeterminedoffset value with a factor for said one form of the control data. 12.The radio transmission apparatus according to claim 1, wherein theoffset value is associated with a parameter of the radio transmissionapparatus.
 13. The radio transmission apparatus according to claim 12,wherein the parameter is a transmission bandwidth, scheduling scheme,frequency hopping or a number of retransmissions.
 14. The radiotransmission apparatus according to claim 1, wherein the offset value iszero.
 15. A radio transmission method comprising: coding one form ofcontrol data using a modulation and coding scheme (MCS) for a radio datachannel and an offset value, the offset value being set for said oneform of the control data; and transmitting data in the radio datachannel and said one form of the control data coded with a coding rateaccording to said one form of the form of the control data.